1. Field of the Invention
The present invention relates to a system for uniformly delivering body coating compositions. More particularly, the invention relates to methods and apparatus for applying such coatings onto the body using the principals of charging, transporting and depositing of electrostatically charged spray droplets.
2. Background of the Invention
Conventional body coating products, whether designed for cosmetic, treatment or medical purposes, are often liquid or viscous or semi-solid products. Most of them are produced in the form of lotions or creams. These products are traditionally applied by gentle massage or rubbing-in with the fingers. These methods of application necessitate the addition of relatively large amounts of adjunct material, i.e. other than the one or more active ingredients necessary to achieve the desired result. Most of these adjunct materials are added to create an aesthetically acceptable product and act as a carrier to deliver the active agent to all parts of the skin. These known delivery systems are wasteful of cosmetic raw materials and have limited efficiency in delivering a desired active ingredient to an intended site. Control over the applied dosage is difficult and limited and the application of the product itself is often time consuming and messy.
In addition, the presence of any significant amounts of stabilizing ingredients such as surfactants, polymers, preservatives, etc, may result in the user experiencing stickiness, greasiness, and possibly irritation. This may be particularly pronounced where skin is damaged or diseased, which may make the application of a product by massage or rubbing-in particularly undesirable.
In the case of coating compositions that are typically applied over the entire body i.e. sun tan lotions, self-tanning products, or moisturizers, application by massage or rubbing-in usually requires a second individual. This is necessary because the user of the product cannot reach and evenly coat all parts of the body unassisted. This is a significant disadvantage because a large percentage of the population would not have such an individual available to apply the product to those hard to reach places.
In addition to the above-described systems for delivering skin treatment agents, there are a small number of known examples where a skin cosmetic or therapeutic active is delivered using an aerosol spray. Two such examples are sprays for sunburn and sprains or other sports injuries. However, aerosol sprays, which are well known in the art for delivering personal products, also suffer from several disadvantages. First, the types of product and active agent that lend themselves to effective aerosol spraying are limited. Second, the use of aerosols still results in significant inefficiency and waste through non-target specific application (over-spray). This over-spray results in loss of active material to the atmosphere. It also creates unwanted mists which can damage surrounding objects if the active ingredient is reactive with whatever object the mist happens to fall on. The use of aerosols to deliver skin cosmetic or therapeutic active agents is also believed to be even less efficient than conventional massage or rubbing-in delivery regimes in the context of percentage and evenness of coverage of the skin surface. Although aerosols can be used to reach many of those hard to reach areas of the body that usually require a second individual for full body application, it is still difficult for a user to achieve a good even coating over the entire body without the assistance of another individual.
The skin is, in fact, a very complex material and has many important characteristics which must be considered in the design of an optimized system for delivering cosmetic or therapeutic actives thereto. For example, skin has a multi-faceted surface having both lipophilic and lipophobic character. This character allows the skin to “breathe” and release water vapor, yet function as an effective barrier against water, dirt and other unwanted materials. One particularly important physical feature of skin is its very rough surface terrain, which creates a problem in successfully applying a desired skin cosmetic or therapeutic active with complete and even coverage.
In a very different technical field, the principle of electrostatic spraying of liquid and solid materials to increase the effectiveness of applying coating materials to objects is also known. In this technique an electrode of the electrostatic nozzle is raised to a relatively high electrical potential to cause the formulation to be emitted as a spray of electrically charged droplets. These electrically charged droplets seek the closest grounded object. Electrostatic spraying techniques have been proposed principally for only large-scale industrial and agricultural applications. Examples of these applications include delivering reactive materials like paints, adhesives, and other surface coatings, as well as large-scale delivery of pesticides and other agricultural or agrochemical formulations.
More recently, there have been a small number of proposals for utilizing the known principle of electrostatic spraying for delivering particular materials in specific applications other than those mentioned above. For example, EP-A-224352 (Ocular Treatment) suggests the use of an electrostatic sprayer for delivering a pharmaceutically active agent to the eye, to replace conventional ocular treatment using eye drops.
Other proposals for applying the principle of electrostatic delivery to the skin, for example, are disclosed in U.S. Pat. No. 5,268,166 (Cosmetic Application System), U.S. Pat. No. 5,494,674 (Skin Treatment System) and U.S. Pat. No. 5,322,684 (Cosmetic Delivery System). Each of these proposals suggests the same method of electrostatic spray application to coat the skin with different types of chemical compositions. In one proposal (U.S. Pat. No. 5,268,166) the coating compositions are color cosmetics, in another proposal (U.S. Pat. No. 5,494,674) the coating compositions are skin treatment agents, and in the final proposal (U.S. Pat. No. 5,322,684) the coating compositions are cosmetically active agents, such as, perfume.
In all three of the above proposals the basic application method outlined is basically the same:
(a) providing an apparatus which includes:                (i) a reservoir containing the coating composition to be delivered which is in an electrostatically sprayable form;        (ii) at least one delivery means which is a nozzle in communication with the reservoir;        (iii) a high voltage generator generating voltage in the range of 2 to 20 kilovolts powered from an electricity source; and        (iv) control means for selectively applying the high voltage from the generator to the at least one delivery means; and        
(b) actuating the said control means to electrostatically spray the coating composition from the at least one delivery means directly onto the skin at an intended site.
The above proposals reference a number of possible “suitable electrostatic spraying hardware” including EP-A-441501 (Electrostatic Spraying Apparatus), EP-A-468736 (Electrostatic Spraying Device and Method), and EP-A-031649 (Containers and Holders Therefor for Use in Electrostatic Spraying). Each of these referenced electrostatic spraying devices are handheld, self contained units where the reservoir, nozzle, generator, and control for applying high voltage from the generator are in the self-contained apparatus. It is apparent from the descriptions of the “suitable electrostatic spraying hardware” that the anticipated use of the methods described in U.S. Pat. Nos. 5,268,166, 5,494,674 and 5,322,684 was to apply the specified coating compositions to the skin on various small, localized areas of the body (e.g., the face) by electrostatically spraying them through a handheld self-contained device.
Although this method of application offers some advantages over aerosol spraying because it would eliminate some of the over-spray problem, it is still difficult to obtain effective uniform coating over the entire body or a substantial portion of the entire body. The uniformity of the coating is impacted by the distance of the nozzle from the skin, the rate of movement of the spray over various parts of the body, the number and intensity of spray bursts necessary to cover the coating area, etc. Because every user will apply the spray differently, each of the variables will vary from user to user and from spray session to spray session. Consequently, the lack of consistency in performance will affect the consumer's acceptance of this product concept.
In another technical field, spray painting, booths have been used to contain spray mists created by air or electrostatic spray painting of objects. These booths prevent the over-spray from landing on surrounding objects that were not part of the desired target. As the art of spray painting booth has evolved one undesirable result, particularly in the case of electrostatic powder painting, has been the coating of the walls of the spray booth which requires labor and down time to clean off. This coating of the booth walls is particularly costly in electrostatic powder coating because the powder adhering to the walls cannot be effectively recycled and the cost of materials is increased.
There have been a number of proposals to resolve this problem of the booth walls being coated. U.S. Pat. No. 5,833,751 (Powder Coating Booth Having Smooth Internal Surfaces) proposes, “a powder coating booth comprising a pair of identical polycarbonate shells disposed opposite each other to define a coating chamber having smooth, curvilinear surfaces to facilitate the recovery and recycle of excess coating powder.”
U.S. Pat. No. 5,277,713 (Cabin for Spray Coating Objects with Powder), for example, describes a cabin for spray coating objects with powder. In the Summary of the Invention it is specified “[w]ith the present invention, the advantages obtained are that the cabin can be produced in a very inexpensive manner, and nevertheless offers greater reliability against electrical arcing, and is electrostatically neutral, or has a repelling effect for many different kinds of powders, so that no or only a few powder particles can collect on the inner surfaces of the cabin.” Moreover, U.S. Pat. No. 5,527,564 (Method and Apparatus for Repelling Overspray in Spray Paint Booths) describes a method and apparatus for repelling over-spray in spray paint booths. In the Summary of the Invention of the '564 patent, it is specified, “[a]mong its several aspects and features, the present invention provides an electrically charged panel which repels electrically charged dry or wet coating particles inside an electrostatic spray painting booth, or other booths having charged paint or powder particles therein.” Later in the Detailed Description of the Preferred Embodiment of the '564 patent it is noted, “Better painting efficiency is achieved because the repelled paint particles will become available to adhere to the articles being painted”.
Until recently, however, prior art in electrostatic spraying technology required that high voltage, 5 to 80 kilovolts, be generated and that the electrostatically sprayable compositions have relatively high resistivity, in the range of 100,000 to 100,000,000,000 ohm centimeters. High voltage types of electrostatic nozzles make aqueous solutions very difficult to spray effectively using electrostatic means due to the highly conductive nature of water-based sprays. Because of the resistivity limitations it was recommended that the compositions be non-aqueous or contain very small amounts of water, e.g., on the order of less than 5%. The non-aqueous solution requirement meant that the most effective and inexpensive carrier for the active coating ingredients could not be used effectively with this process. In addition, the high voltage requirements made electrostatic spraying of coating materials on the human body too dangerous to be seriously considered.
However, recently there have been innovations in the field of electrostatic spray nozzles that have made this process more acceptable for the application of coating compositions in various fields such as industrial and agricultural applications. For example, U.S. Pat. No. 5,765,761 (Electrostatic-Induction Spray-Charging Nozzle System) and U.S. Pat. No. 5,704,554 (Electrostatic Spray Nozzles for Abrasive and Conductive Liquids in Harsh Environments) describe “air atomizing induction charging spray nozzles suitable for use with conductive liquids, solutions, suspensions or emulsions”. The major advantage of the described method is the high level of spray charging that can be achieved at very low electrode voltages and power. The total power required is very low, typically less than 0.5 watts per nozzle with very conductive water-based spray liquids. The introduction of this new air-assisted induction charging system (AAIC), which operates with low voltage and low current, makes it possible to utilize electrostatic spraying to create an electrostatic mist that could be used to apply a coating composition to the human body without any risk of electrical hazard to humans.
The typical approach to developing conventional uncharged automated spray tanning systems has been to mount many nozzles at various heights or angles around the subject in an effort to apply an even coating. Typically, the customer is instructed to move through a variety of poses during the spray event which usually lasts less than 30 seconds. With these conventional spray methods there are often less than optimum tanning results due to missed or thinly coated areas, and dark runs and streaks occur from over application. Presently used tanning compounds are expensive and the poor spray deposition efficiency reduces the profit margins of the spray tanning system. Less than optimal mass transfer of the tanning compound results in a light tanning color that fades more quickly than a heavier initial application. In addition, even though the tanning compounds are safe materials, the level of respirable aerosols can be high during and after the spray process and may be irritating to some customers. If ventilation is poor, lingering aerosols can be carried throughout the salon and create high levels of unwanted dust deposits on store fixtures.
U.S. Pat. No. 6,387,081 (Misting Apparatus For Application Of Coating Materials To Skin Surface) describes an apparatus and method for electrostatically coating a human with a coating composition. An embodiment of U.S. Pat. No. 6,387,081 includes an enclosure; a mount positioned on the enclosure; an electrostatic nozzle connected to the mount, the electrostatic nozzle for passing the coating composition; and a grounding connection positioned inside the enclosure, the grounding connection capable of directly electrically grounding the human, wherein the coating composition is depositable upon the human. This prior art electrostatic spray system provides a conductive plate, with a wire directly connected to ground. A human subject stands on this plate during the spray process. The plate serves to electrically earth the human spray target with a negligible resistance from plate to earth (i.e. less than 1 ohm). The presence of the directly-grounded metal plate contacting the feet and adjacent to the sides of the feet can cause preferential deposition on the feet and ankles due to the increased electric field strength in these areas. In addition, whole-body spray uniformity may be affected due to the head-to-toe potential gradient that forms during charge transfer of spray over the resistive skin surface of a human target standing on a directly grounded metal plate. An electrically resistive floor would serve to slow charge decay time, slightly elevating the electrical potential of the target and reducing the electrical potential difference between upper and lower body portions. If the resistance between the feet and earth is significantly greater than the overall human body resistance, electrical potential would be beneficially equalized from head to toe. Human body skin surface resistance from head to toe is normally in the range of 200 k ohms. Therefore, a resistive ground of greater than 10 times the target body resistance (i.e. 2 megaohms) would be sufficient to equalize potential differences from head to toe.
In addition, it would be desirable to maintain resistance of the human subject to earth in the range of 105 and 109 ohms for safety. This resistance range is sufficient to allow adequate charge transfer for electrostatic spray deposition without significant charge accumulation, yet will provide protection in the case of accidental contact with electrical mains. (JA Cross—Electrostatic Principles, Problems and Applications, Adam Hilger Publishing Bristol, England 500 pages, 1987, ISBN 0-85274-589-3). However, it should be noted that commercial versions of U.S. Pat. No. 6,387,081 operate on reduced voltage, and this design prevents the chance of human contact with the mains voltage while the human subject is standing on the grounding plate.
Although satisfactory results have been obtained using the invention of U.S. Pat. No. 6,387,081, in accordance with the present invention it has been determined that very satisfactory results can be obtained without directly grounding the human spray target. The present invention provides for a method and apparatus for electrostatically coating a human with a coating composition which provides for improved mass transfer and uniformity of spray solution onto the body. An additional advantage of the present invention is that it provides for a reduction in the level of respirable aerosols present in the spray environment.